Transcript Short-range, high-LET recoil tracks in CR

Short-range, high-LET recoil tracks in CR-39
plastic nuclear track detector
E. R. Benton1, C. E. Johnson1, J. DeWitt1, N. Yasuda2, and
E. V. Benton3
1Dept.
of Physics, Oklahoma State University, Stillwater, OK 74078 USA
2National Institute of Radiological Sciences, Chiba, Japan
3Dept. of Physics, University of San Francisco, San Francisco, CA 94117 USA
Integral LET Fluence Spectra
60, 230, & 1000 MeV Protons on CR-39 PNTD
10-2
2
Particles(> LETH2O)/(cm proton)
10-3
10-4
10-5
10
60 MeV (LLUMC)
230 MeV (LLUMC)
1 GeV (NSRL)
-6
10-7
100
101
102
LET H2O (keV/mm)
103
CR-39 PNTD: 36 hr etch in 50°C, 6.25 N NaOH, B =~8 mm
Proton- & Neutron-Induced
Target Fragment Reactions
Target CR-39 PNTD
incident high energy
proton (or neutron)
n
Intra-nuclear
Cascade

knock-out particles
p
n
evaporation p
nucleons p
n
Recoil Heavy
Fragment
Contribution to Dose and Dose Equivalent from
Proton-Induced Target Fragmentation
LLUMC Proton Therapy Beam, Bragg Plateau
Proton
Energy
Total
Dose
(mGy)
80
175
223
139  11
95  7
101  8
•
•
•
Dose from Contribution to
Total
Target
Total Dose from
Dose
Fragments
Target
Equivalent
(cGy)
Fragments
(mSv)
4.1  0.3
4.3  0.3
4.2  0.3
3.0 %
4.5 %
4.1 %
180  18
134  12
148  15
Dose
Equivalent
from Target
Fragments
(mSv)
45  4
44  4
51  5
Contribution to
total Dose
Equivalent from
Target Fragments
25.5 %
32.5 %
34.3 %
Contribution of high LET (5 keV/mm) particles to
dose ranges from 3 to 4.5%
The contribution of high LET particles to the dose
equivalent ranges from ~25 to ~35%
Only includes fragments with range >8 mm... shorter
range fragments are not included.
CR-39 PNTD Exposures for AFM Analysis
CR-39 PNTD
Target
Incident
Beam
H6He-#XX
sensitive side
Side View
Top View
10 µm x 10 µm
• CR-39 PNTD: 2-4 hr etch in 50°C, 6.25 N NaOH 
B = 0.5-1.0 mm
• Primary Proton Fluence: ~1010 cm-2
31010 cm-2 1 GeV Protons on CR-39 PNTD
4 hr etch, 1 mm removed, 103  79 mm2
Short-Range, High-LET Recoil Tracks
in CR-39 PNTD
Light Microscopy Exposure:
AFM Exposure:
For Comparison:
108 cm-2 230 MeV Protons
1.5  1012 cm-2 1 GeV Protons
108 cm-2 1 GeV/n Ti
36 hr etch, 8 mm removed
4 hr etch, 1 mm removed
4 hr etch, 1 mm removed
328  253 mm2
103  79 mm2
103  79 mm2
No track >100 keV/ mm
(~100 keV/ mm)
1.51010 cm-2 230 MeV Protons on CR-39 PNTD
Long, Shallow Recoil Tracks
Short, Dark Recoil Tracks
Track "tails" from recoils
produced deeper within
the target or detector
4 hr etch, 1 mm removed, 103  79 mm2
Stopping Particles, Low Enery Scattering
1 GeV Protons on Au Target
Proton-induced Target Fragmentation as
functions of Target Z and Energy
CR-39 (12C &16O)
60 MeV
(LLUMC)
230 MeV
(LLUMC)
1 GeV
(NSRL)
27Al
28Si
64Cu
108Ag
197Au
Normalized Fluence (tracks/cm2 particle)
Target Fragment Fluence as functions of
Proton Energy and Target
10-5
10-6
10-7
Au
Ag
Cu
Si
Target
Al
CR-39
60 MeV Protons
230 MeV Protons
1 GeV Protons
150 MeV/n 4He
Fragment Distribution as a Function of Angle
230 MeV Protons (LLUMC)
Normalized Fluence (tracks/cm 2 proton)
5E-7
CR-39 PNTD
Gold
4E-7
3E-7
CR-39 PNTD perpendicular
to proton beam
2E-7
1E-7
-180 -150 -120 -90 -60 -30
0
30
60
Incident Angle (degrees)
90
120 150 180
Integral LET Fluence Spectra
230 MeV Protons on CR-39 PNTD
2
Particles(> LETH2O)/(cm proton)
10 -3
10 -4
10 -5
10 -6
Optical Scan (B = 8 mm)
AFM Scan (B = 0.5 mm)
10 -7
10 -8
10 0
10 1
10 2
LET H2O (keV/mm)
10 3
AFM CR-39 PNTD: 2 hr etch in 50°C, 6.25 N NaOH, B = 0.5 mm
Integral LET Fluence Spectra
1 GeV Protons on CR-39 PNTD
2
Particles(> LETH2O)/(cm proton)
10 -3
10 -4
10 -5
10 -6
10
Optical Scan (B = 8 mm)
AFM Scan (B = 0.5 mm)
-7
10 -8
10 0
10 1
10 2
LET H2O (keV/mm)
10 3
AFM CR-39 PNTD: 2 hr etch in 50°C, 6.25 N NaOH, B = 0.5 mm
Conclusions from Light Microscopy Analysis
of CR-39 PNTD AFM Exposures
• The heavy recoil tracks often take the form of long tubes,
not short cones. Tube-shaped tracks are characteristic of
extremely high LET (>1000 keV/mm) particles near the
end of their ranges.
• Some tracks “zig zag” toward their ends, illustrating range
straggling.
• Some tracks are “forked”, illustrating low-energy
Rutherford scattering.
• The size of the tracks (width and length) scales with Z of
the target material.
• Fluence (and production cross section) scales with proton
energy.
• Preliminary measurements appear to show that the angular
distribution of high Z recoil fragments is isotropic.
Relevance/Applications
• Nuclear Physics: Validate Nuclear Reaction Models
• Provide Data to Extend Radiation Transport Codes
• Proton and Heavy Ion Therapy
• Radiation Effects on Electronic Circuits
• Space Radiation Dosimetry
• Study of Neutron Interactions with Heavy Nuclei
Conclusions
• Tracks from proton- and neutron-induced short-range (<20
mm), high-LET recoil fragments in CR-39 PNTD are
visible through a standard optical microscope for Bulk
Etch of 0.5-1.0 mm.
• New method to quantify heavy recoil nuclear processes
previously not accessible due to short range of fragments.
• LET spectra measured by AFM consistent with previous
LET measurements made by standard light microscopy.
• Extend work to other targets, different proton energies,
heavy ions, and medium and high energy neutrons.